Epstein-Barr Virus (EBV) is a human tumor virus causally associated with several lyrnphomas and carcinomas. It efficiently induces and maintains proliferation of the B-lymphocytes it naturally infects until the immune response can limit that infection. EBV's proliferative effects on infected cells likely underlie its pathogenicity. One of the few EBV genes contributing these proliferative effects is its latent membrane protein-1 (LMP-1). LMP-1 is found at the plasma membrane where its carboxy terminal domain associates with several cellular signaling molecules which are also bound by TNF and CD40 receptors. LMP-1's signaling domain has been studied extensively in cells in the absence of other viral genes. It has also been studied in recombinant EBV's which for technical reasons have allowed only qualitative findings. We have developed a means to isolate pure recombinant EBV's, termed "maxiEBV's," with high titers allowing us to assess quantitatively individual elements of LMP-1 in transformation assays. We hypothesize that multiple activities of LMP-1 contribute to its efficient signaling to support EBV's induction and maintenance of proliferation of infected cells. We shall test this hypothesis genetically with maxi-EBVs in Aim I and by identifying the cellular genes which are the immediate targets of LMP- l's distinct signaling activities in Aim IV. LMP-1 signals in the apparent absence of a ligand with its six membrane spanning domains supporting its aggregation in lieu of that contributed by ligand-binding. It traffics to the plasma membrane and to membrane rafts where it is found as a signaling complex again in the apparent absence of a ligand. We hypothesize that LMP-1 represents a currently undefined solution to the problem of regulating signaling. We shall test this hypothesis by elucidating the path by which LMP-1 transits to the plasma membrane, the moieties it requires for aggregation, and the temporal order and requirements for it to move to membrane rafts and form a signaling complex in Aims II and III. These studies will be confirmed and extended genetically with maxi-EBVs to place them in the context of infection with EBV. All of the proposed research will quantify the contributions of known activities and new activities of LMP-1 that it provides EBV's infected cells.